Brachyponera chinensis (Emery, 1895)

Menchetti, Mattia, Schifani, Enrico, Gentile, Vincenzo & Vila, Roger, 2022, The worrying arrival of the invasive Asian needle ant Brachyponera chinensis in Europe (Hymenoptera: Formicidae), Zootaxa 5115 (1), pp. 146-150 : 146-147

Brachyponera chinensis

is considered a taxonomically challenging species, and past confusion over its distinction from congeneric species still hinders a full understanding of its distribution in Asia ( Guénard et al. 2018). It is considered to be part of an unresolved species complex, characterized by high intraspecific morphological variation ( Yamane 2007; Yashiro et al. 2010). The revision carried out by Yashiro et al. (2010), mainly based on Japanese and Taiwanese material, distinguished three species using molecular and morphological data: B. chinensis , B. nakasujii Yashiro et al., 2010 , and B. luteipes (Mayr, 1862) , whose ranges considerably overlap.

Regarding Europe, the only existing record is a reported interception in Hamburg ( Germany), on plants shipped from Japan, which dates back to the year 1900 (reported as Ponera solitaria by Forel (1900)). However, given the taxonomic confusion reigning at that time, the identity of the species recorded by Forel (1900) is uncertain.

In this paper, we present the first confirmed record of B. chinensis for Europe, initially suggested by morphological characteristics, and then confirmed by genetic analysis (DNA barcoding). A single specimen of an unidentified male belonging to the genus Brachyponera was collected while attracted to a streetlight on the 3rd of July 2020 by one of the authors (VG) in Torre Annunziata (Naples, Italy), in a residential area about 1 km from the town harbour , at the coordinates 40.758824, 14.434152 (uncertainty ± 10 m, 32 m a.s.l.). The specimen is stored at the Butterfly Diversity and Evolution Lab, Institute of Evolutionary Biology ( CSIC-UPF) (Barcelona, Spain) under the voucher code MM21B056a1.

A first morphological investigation revealed that the specimen differed from any native Euro-Mediterranean ponerine genera and matched Brachyponera instead by features such as the ventral cuticular processes of the metasternum and petiole ( Figure 1c ). Moreover, the male specimen corresponded to B. chinensis by its light coloration and mandible shape ( Yashiro et al. 2010). However, like in most ant genera, Brachyponera taxonomy is mostly based on workers, with detailed male-based keys missing and males are undescribed for at least half of its 23 described species ( Bolton 2022). As a result, an accurate and definitive identification on the basis of morphological features only was not possible.

Four legs of the specimen were removed for genetic analysis and sent to the International Barcode of Life project (iBOL) ( deWaard et al. 2008). A DNA-barcoding (mitochondrial gene cytochrome c oxidase subunit I, COI) sequence of 658 bp was obtained using the primers LepF1 and LepR1 ( deWaard et al. 2008) and submitted to GenBank (accession number OM604749 ). For the genetic identification, we retrieved a total of 17 sequences of five Brachyponera species from GenBank: B. chinensis (accession numbers GQ264540 , GQ264547 , GQ264550 , GQ264554 , GQ264561 , GQ264562 , GQ264565 , GQ264566 , GQ264570 from Yashiro et al. 2010 and MT800254 , MT800255 , MT800256 from Park et al. 2020), Brachyponera luteipes (Mayr, 1862) (a.n. GQ264575 , GQ264582 , GQ264583 from Yashiro et al. 2010), B. nakasujii (a.n. GQ264583 from Yashiro et al. 2010), Brachyponera nigrita (Emery, 1895) (a.n. GQ264596 from Yashiro et al. 2010) and Brachyponera obscurans (Walker, 1859) (a.n. EF609925 from Smith & Fisher 2009).

Sequences were edited and aligned with Geneious 2020.2.4 (www.geneious.com) and a neighbour-joining tree was built with the same program, using Ectomomyrmex javanus Mayr, 1867 as outgroup (a.n. GQ264573 from Yashiro et al. 2010). A haplotype network of B. chinensis sequences was built with the program TCS 1.21 ( Clement et al. 2002) and later edited with tcsBU ( Múrias dos Santos et al. 2016) and Adobe Illustrator CC 2019. The genetic analysis confirmed the single male as B. chinensis with high support (99% bootstrap value) ( Figure 1d ). The COI haplotype found in Italy is the same previously reported in the USA, suggesting a possible origin from this country or a common source of introduction ( Figure 1e ).

Besides the potential problematics related to the use of barcoding for ant species delimitation (e.g. Schifani et al. 2021) and identification (e.g. Blatrix et al. 2020), here this technique helped us determining a potentially established population of the highly invasive species B. chinensis , based on the taxonomic framework by Yashiro et al. (2010).

As many other soil invertebrates, ants are often accidentally introduced in new environments due to the ongoing globalization and in particular to the plant trade ( Pyšek et al. 2020). Their frequent introduction in private gardens or greenhouses can facilitate their recording when the species are particularly charismatic and easy to spot (e.g. through citizen science, Mori et al. 2021), but it can also make the field surveys harder to be carried out. The latter one is probably the case for B. chinensis in Torre Annunziata (Naples, Italy): an area of 300 m of radius around the site where the specimen was found, as well as the area of the harbour, have been surveyed multiple times from 2016 to 2021 and no other individual belonging to this species have been found. More surveys, perhaps employing specific traps, will be useful to further verify the presence of nests. The fact that we collected a swarming male points to three potential concerns: a) At least one nest is already in an advanced stage and the species may have already overcome the typical “lag phase” after introduction and during establishment, preceding the increase-phase marking spread ( Pyšek et al. 2020). This is problematic considering that the high inbreeding tolerance of B. chinensis may allow a few foundresses to give birth to an entire population ( Eyer et al. 2018). b) Since the dispersal capabilities of B. chinensis are undocumented, and it may disperse by independent foundations, including through pleometrosis (Benoit Guénard pers. comm.), it is hard to locate the nest of origin and eradicate it. In fact, the nest of origin may be in hardly accessible private areas and the colony (or colonies) may have time to spread while remaining undetected. c) A queenless colony may have been introduced and males were produced by the workers, capable of laying haploid eggs in the B. chinensis complex ( Gotoh & Ito 2008).

The Mediterranean basin hosts an increasing number of exotic species, but most of them have remained limited to indoor or at least urban environments ( Schifani 2019). Climate change may also play a significant role for the establishment of B. chinensis in Italy ( Bertelsmeier et al. 2013). However, the success of B. chinensis in North American forest habitats suggests that this species could potentially invade European natural habitats and particularly forests, likely affecting native communities. On the other hand, its establishment in urban areas may constitute a public health concern ( Nelder et al. 2006). We call for action at the presumably early stage of this new potentially harmful biological invasion and propose that a detailed survey of a wide area around Torre Annunziata is conducted.

Figures

FIGURE 1. Lateral view (a), frontal view of the head (b) and a close-up lateral view of the petiole (c) of the specimen of Brachyponera chinensis collected and sequenced. d) Neighbour-joining tree based on mitochondrial COI sequences, the new record is indicated with a star, bootstrap values above 75 are shown on the branches and the species names, countries and Gen- Bank accession numbers are indicated in the tip labels; e) Haplotype network of B. chinensis COI sequences, colours indicate the sample origin and sizes of the circles the number of samples.